1. Field of the Invention
The present principles relate to optical disc authentication. More particularly, it relates to a method and apparatus for disc authentication by applying a grayscale image in the data area through modulation rule variation.
2. Description of the Related Art
The modulation rules applied when writing an optical disc are of integral importance when considering copying and unauthorized duplication of the same. Existing binary systems for imaging the data portion of an optical disc have been shown, for example by the Philips Electronics Pit O' Resc system. This system provides a modulation scheme and hardware that enables a binary image to be encoded on the data portion of the disc so as to generate an image on the same.
Binary images have significant limitations in the art, and more particularly do not provide sufficient flexibility so as to provide more than two diffraction patterns (i.e., more than 2 grayscale levels) in order to decrease forging and counterfeiting capability by adding significant more detail to the authentication images applied there to.
It is therefore desirable to have features on an optical disc which are easily visible with the bare eye and are hard to forge, so that it is easy to determine if it is a legitimate replicated disc or a pirated one.